Variable buoyancy systems are commonly employed in salvaging objects from the ocean or positioning and recovering oceanographic instrumentation. These buoyancy systems may take several different forms, such as lift bags or ballast tanks. Historically, high-pressure air tanks have been utilized for deballasting such buoyancy systems. More recently, various materials have been reacted to generate a gas for deballasting the systems. Hydrazine is commonly reacted to generate a gas, and has been found highly satisfactory for raising objects from the ocean bottom. However, hydrazine is not cost effective and is very hazardous for personnel to handle.
Gas generated by reacting metallic hydrides is safer and considerably more cost effective than hydrazine. However, prior art metallic hydride gas generators could not be sufficiently controlled to perform their intended job functions. The specific problem associated with such prior art gas generators is in the starting and stopping of the reaction.In U.S. Pat. No. 4,055,632 to Robert T. Hoffman there is shown a controllable gas generator which utilizes metallic hydride pellets which are selectively released from a nonreactive liquid to a reactive liquid for the generation of gas. This generator is satisfactory for raising small objects, however, a more practical system is required for raising large objects from the ocean bottom. Also, the gas generator described in the patent will not terminate the generation of gas quickly since the pellets must be completely expended once they are disseminated into the reactive liquid.